Such a BBW (brake by wire) brake device has already been known from Patent Document 1 below.
In this BBW brake device, a slave cylinder is caused to generate a brake fluid pressure corresponding to a braking force required by a driver: by carrying out a map search for a brake fluid pressure to be generated by the slave cylinder, on the basis of a pedal stroke of a brake pedal depressed by the driver; applying this brake fluid pressure to a brake-fluid-pressure/slave-cylinder-stroke map based on load fluid loss characteristics to thereby convert the brake fluid pressure to a piston stroke of the salve cylinder, and performing a feedback control for a rotation angle of an electric motor of an actuator for the slave cylinder so as to generate the piston stroke.    Patent Document 1: Japanese Patent Application Laid-open No. 2008-110633